Heart transplantation is the preferred therapy for patients with a variety of end-stage heart diseases. Over the last two decades, developments in immunosuppressive medications, technical innovations, and improvements in postoperative care have significantly improved outcomes following heart transplantation. Cardiac allograft ischemia-reperfusion (I-R) injury, however, remains a major source of morbidity and mortality leading to both early allograft dysfunction as well as long-term morbidity. Considerable evidence supports an important role for heme oxygenase (HO-1) in protection against I-R. This enzyme catabolizes heme into biliverdin, free iron and carbon monoxide (CO), which act to reduce inflammation and cell death. The goal of this proposal is to develop suitable HSV-HO-1 gene vectors that specifically target infection of heart blood vessel endothelium and express HO in sufficient levels and duration to ameliorate this type of ischemic disease. In four specific aims, a retargeted HSV vector (HSV-HOT) will be engineered in which the endothelial-specific receptors VEGF-R2 (vascular endothelial growth factor receptor) [and/or Tie-2 (angiopoietin receptor)] will be used for virus attachment and penetration in lieu of the natural HSV receptors HveA and HveC. If needed, we will also explore an alternative retargeting strategy that utilize a targeting soluble adapter (Aim 1). A highly engineered, replication defective vector backbone will be used for gene delivery. This vector is noncytotoxic, highly stable, capable of vigorous transgene expression and suitable for high titer manufacture and purification using cell lines that are engineered to complement the defective viral functions in trans. Preclinical studies will be carried out in vitro using human endothelial cells (Aim 2) followed by in vivo studies in rodent (Aim 3), pig and primate (Aim 4) heart transplantation models. Vector application studies will include the development of procedures for vector administration to heart blood vessels, analyses of vector dosing and distribution, characterization of HO-1 expression and byproduct synthesis (e.g. CO), and evaluation of protection from I-R. It is our long-term goal to develop the preclinical efficacy and safety data needed to perform early phase I trials in heart transplant recipients.